As the others said very well -- it varies WIDELY depending mostly on how much you are paying for components and exactly what kind of loads you intend to make. That's because the bullet is the most expensive part (in a handgun round, anyway) and the bullet is the biggest determining factor in what kind of ammo you hope to produce.
But a quick couple of shortcuts may help you as you ponder the idea...
First is that the cheaper and more popular the factory ammo is, the less advantage (money-wise) you have when you handload. The world's finest example may forever be 9mm. A good shopper can bring home a box of DECENT, name brand 9mm for around $12 a box if they find a decent sale. Now me, making fantastic 9mm, but buying a (ridiculous!) volume of my components in bulk to keep my costs down, can produce a box of ammo that I know for sure is as good/BETTER, and it costs me about $5.50.
Now .357, .44 Mag?
.460 S&W Mag?!
Well, I can save a ridiculous pile of money because that ammo goes for a crazy price tag. Figure like $25 a box for .357. I see .44 Mag going for $35.
.460 Mag?! Let's not even go there. Okay... what it is, like $40 a box for 20rds?!
Now, keep in mind...
My costs are going to be lower than yours if you start because I buy components in bulk. Honestly, my costs are going to be lower than most folks posting here, except for the guys who cast their own slugs. Keeping costs down is a
game and it's a game that I play because I can and it makes sense to me. So when I have the opportunity to buy bullets for a good price, I spend the kind of money on them that a lot of people couldn't possibly even justify spending for a new handgun.
The bottom line is that your "cost" for ammo will drop significantly if you jump in to handloading. The net result is almost 100% guaranteed, however, to be you
spending more money handloading than you EVER did on ammo. It's natural, because you will make ammo and want (and need!) to shoot it, and you'll spend money on handloading tools and accessories, etc.
If you are on a shoe string budget, it may not be for you. But it is something I enjoy as much/more than shooting.